Lubricating grease composition for missile systems



United States Patent No Drawing. Filed Oct. 15, 1963, Ser. No. 316,478 21 Claims. (Cl. 252--28) The invention described herein may be manufactured and used by or for the Government for governmental purposes without the payment to me of any royalty thereon.

The present invention relates to improved grease-type lubricants. More particularly, the invention concerns improved grease-type lubricants compatible with missile fuels and oxidizers and the preparation thereof.

In the field of rocketry and missiles and particularly in the technological development of liquid fuel powered rorket motors, considerable work has been done in an effort to provide satisfactory lubricants for the moving parts thereof, including reduction gears, turbine pumps, gimbal bearings, and valves. Heretofore, prior art lubricants, both grease-type and oil-type, have proven unsatisfactory primarily because of their undesirable reactivity or solubility characteristics. Reactivity with liquid fuels and oxidizers poses the danger of malfunction either in the form of interference with operation of a lubricated part or initiation of a destructive chemical reaction. In either event, loss of the entire rocket system may result. Solubility of the lubricant in the fuel or oxidizer is also undesirable, but precise solubility limits have not been established and the extent to which very slight solubility may cause malfunction depends on the particular material systems combination. In addition to the material requirement, consideration must also be given to other properties associated with lubrication such as lubricity, anti-wear, and load carrying capacity; and other physical and chemical properties which determine long term stability and usefulness over a wide temperature range. Since conventional lubricants such as petroleum, dicarboxylic acid esters, silicates, silicones, and polyglycols are either miscible with the fuels, and reactive or explosive at high impact energy levels with the oxidizers, it is obvious that they may not be used as lubricants for rocket engines.

Accordingly, a principal object of the present invention is to provide improved grease-type lubricants unattended by the foregoing disadvantages of the prior art.

Another object of the invention is to provide improved grease-type lubricants compatible with contemporary missile fuels and oxidizers. The term compatible as used here has reference to insolubility and non-reactivity.

A further object of the invention is to provide a method for the preparation of improved grease-type lubricants exhibiting compatibility with fuels and oxidizers presently encountered in liquid fuel-powered rocket motors.

Other objects and advantages of the invention will in part be obvious and in part appear hereinafter in the following detailed description of the principles of the invention and several of the embodiments thereof.

The present invention embodies grease-type lubricants comprising a mixture of mixed perfluorotrialkylamines (alkyl=C through C with tetrafluoroethylene polymers having a molecular weight in the range of 2,000 through 3,262,879 Patented July 26, 1966 30,000, graphite or silica. The inventive lubricants are characterized by excellent physical stability as evidenced by no visible fluid separation on standing for periods up to one year and little separation in cone tests at 100 C. for a period of 30 hours, compatibility with contemporary missile fuels and oxidizers as evidenced by non-reactivity with and insolubility in ethyl alcohol, hydrocarbon fuel, unsymmetrical dimethylhydrazine, diethylenetriarnine, a 60:40 mixture of unsymmetrical dimethylhydrazine and diethylenetriamine, aniline, a 50:50 mixture of unsymmetrical dimethylhydrazine and hydrazine, hydrazine, 90% H 0 inhibited red fuming HNO and N 0 and no explosive reactivity as evidenced from impact tests with liquid oxygen (LOX) and N 0 Anti-Wear and extreme pressure properties of the inventive lubricants are comparable to conventional petroleum and synthetic greases, and conventional elastomers may be employed in contact therewith Without noticeable reactivity.

In the course of the investigation leading to the present invention various grease-type lubricants were prepared by dispersing a thickening agent in a base fluid. The base fluid used was a mixture of mixed perfiuorotrialkylamines in which the alkyl groups varied from C through C Typical properties of this fluid were as follows: boiling range, 230300 0; density at 25 C., 1.9; viscosity at 25 C., 141 cs.; pour point, 20.6 C.

The thickening agents employed were all tetrafiuoroethylene polymers having an average particle size of 5 microns, graphite having an average particle size of 2.5 microns, and silica having an average particle size of 9-14 millimicrons. Table I lists the various tetrafluoroethylene polymer thickening agents studied.

TABLE I Thickeners Avg. M01. Wt. Percent 01 999999992-2-9 ocooomenoooc: Hut 0 In preparing the inventive lubricants, samples of thickeners from Table I dispersed in a solvent of trichlorotrifluoroethane were heated on a steam 'bath. Evaporation of 50-75% of the solvent resulted in the obtention of a viscous dispersion of the consistency of glycerol. Base fluid was then added in two stages: of the required quantity being added initially with stirring and heating until complete evaporation of the solvent; the remainder being added thereafter with continued stirring until obtention of a homogeneous grease-like product. The mixture was then cooled to room temperature with stirring, immersed in a bath at -75 C. for 30 minutes, and permitted to remain at room temperature overnight. It is important to note that if the solvent is permitted to evaporate completely before adding the base fluid, a stable, grease-like product cannot be obtained. Table 11 sets forth the compositions of the various grease-type I lubricants prepared.

TABLE II Grease Base Fluid, Thickcner,

Percent Percent 71.8 T-20, 28 2 72.4 T45, 27 6 80.0 T-50, 20 80.6 T-100, 19 4 82.0 T-300, 18.0. 85.0 Graphite, 15.0. 90.0 Silica, 10.0.

TABLE III.SIIEAR STABILITY AND FLUID SEPARATION Grease Unworked Worked Separation,

Penetration Penetration 11 Percent a After 500 strokes in the scale worker.

Contact compatibility tests were run at 25:1" C. using the method similar to that described by Fisch et al., ASLE Trans., 5, 28 (1962). Preliminary experiments 24, 48 and 72 hours, respectively. The fuels and oxidizers used in the tests were ethyl alcohol (EtOH), hydrocarbon fuel (JP-4), unsymmetrical dimethylhydrazine (UDMH), diethylenetriamine (DETA), a -40 blend of the last two (U-DETA), aniline, a 50-50 blend of unsymmetrical dimethylhydrazine and hydrazine (U-H), hydrazine (N H 90% -H O inhibited red fuming nitric acid (IRFNA), and nitrogen tetroxide (N 0 The tests using N 0 were run in closed 1 x 5 in. pressure glass jars. (Liquid oxygen, LOX, impact tests were run at a single impact energy level. N 0 impact tests were run at 400 ft.-lbs./in. if there were any failures in 10 trials, tests were repeated at lower energy levels. It should be noted that different units are used for impact levels and that the numbers are not directly comparable.)

The results of the contact compatibility tests are given in Tables IV and V. Earlier data indicated that compounds containing appreciable chlorine are not inert with the amines. This was again observed here. Compounds having 0.5% or more chlorine showed some reactivity with the amines. However, compounds T-100A, T-120, and T-250 although having no chlorine (0.03% for T-ZSO) showed some reactivity with UDMH, and also some swelling with EtOH and JP-4. It is not known whether this is due to an impurity or some preparation variable (i.e., polymerization catalyst, terminal group, etc.).

From Table V, it is noted that although the perfluoroamine is soluble to the extent of 25% in N 0 nevertheless there was no apparent effect of N 0 on the grease. After evaporation of the N 0,, from its mixture with the grease, the latter appeared completely unchanged. Evidently, the structure of the grease dispersion is such that the fluid is not readily accessible for solution.

TABLE IV.CONTAOT COMPATIBILITY TESTS OF THICKENING AGENTS Material EtOH .TP-4 UDMH DE'IA U-DETA Aniline U-II N2H4 H1O; IFRNA N104 I I C C C I O R I R I I I C R R I R R I C C I I C C O C C C I I I I I I I I I I I I I I I I C I C I C O I I I M I O I C I I I I I I I I I I I I I I I I I M M C I C I I I I I I I I I I I I I I I I I M M C I O I I I I I I I I I I I I I I I I I I I I I I SOC I I S I I I I I I R I I I-no apparent change, C-eolor change, M-swell, R-gas formation, SCC-slight color change, Sslu.rry.

TABLE V.CONTACT COMPATIBILITY TESTS OF THE GREASES AND BASE FLUID Material EtOH J P-4 UDMH DETA U-DETA Aniline U-II N H14 H10; IFRNA N 204 I I C C C I S O I I S S S S C O C O C I I S I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I S I I I I I I R I S I I I I I I I I I I Y I-no apparent change, C-color change, R-gas formation,

were first run on approximately 0.03 gram of thickening agent to insure that there was no explosive reactivity. When there was no immediate reactivity, tests were continued using suitable precautions against later reactivity. To 1.0 ml. of test reagent (fuel or oxidizer) in a 5 ml. graduated cylinder there was added approximately 0.03 gram of thickening agent with thorough shaking and observation for solubility or reactivity. If there was no evidence of solubility or reactivity, further increments were added with shaking until a total of one gram of gelling agent was used. If no reaction occurred, -a one gram sample of the grease was placed in a 5 ml. graduate and one ml. of fuel or oxider added. Visual observations preceded by shaking were made after 5 minutes, and 1,

Sslurry, Y-soluble (25%).

The impact compatibility tests were run with LOX and N 0 using the method of Marshall Space Flight CenterfiSpecification 106, Compatibility Testing, Liquid Oxygen Systems and Materials for LOX and the Method of Kopituk, ASTM Bull., No. 250, 51 (Dec. 1960) for N 0,. Materials were considered nonreactive with LOX if they withstood 20 separate impact trials without reaction (flashes, explositions, or other indications of sensitivity) at an energy level at 72.3 ft.-lbs. Materials were considered nonreactive with N 0 if they withstood 10 separate impact trials at 200 ft.-lbs./in. minimum without reaction. The impact compatibility data, Table VI, show that all the materials tested are not reactive with LOX and N 0 within the mentioned limits. It is noted however, that the reactivity of grease 6-50 is somewhat lower than its thickening agent, T-SO. To the extent that this difference is significant, the fluid appears to exert a shielding effect on the thickening agent.

TABLE VI.-IMPAOT COMPATIBILITY TESTS Material LOX Notgeaetive.

* Maximum impact level (ft.-lbs./in. for no reaction in 10 trials.

the lubricants as thread lubricants in addition to other applications.

TABLE VII.REACTIVITY OF GREASE G-50 WITH METALS AT HIGH SHEAR Load-100 lbs. at 1,760 rev./min. b Also tested at 00 lbs. and 500 rev./min. with the same results.

TABLE VIII.LUB RICAN'I PROPE RTIES Property G-50 G-lOO G-300 B E Dropping point, C 150 117 Evaporation loss, percent 47. 0 4.4. 9

Neutralization number .00 .05

Water washout at 373 0., 19. 5 15. 7

percent Oxidation stability No pressure drop, no No pressure drop, no N 0 pressure drop, no 2 lbs. drop, no decom- No pressure drop, no Pressure drop, 100 hrs. decomposition of decomposition of decomposition of position of grease. decomposition of at 121.2 C. grease. grease. grease. grease.

Copper strip, hrs. at No pressure drop, no No pressure drop, no No pressure drop, no No pressure drop, no No pressure drop, no

l21.2 0. discoloration of discoloration of discoloration of discoloration of discoloration of grease or strip. grease or strip.

grease or strip. grease or strip. grease or strip.

ASTM D566. ASTM D972. AS'IM D974.

' here, tests were run on 6-50 in the following manner.

Approximately 5 grams of grease were placed in a cylin- ASTM D1264.

ASIM D942. ASTM D1402.

In Table VIII are given the physical and chemical properties of the greases. The limiting property may be volatility, which may limit the use of the grease to relatively short time-high temperature combinations. (Precise limits for any application would have to be determined for the particular case.) Although no low temperature viscosity data are as yet available on the greases, the pour point of the fiuoroamine fluid is 20.6 C. which gives a first approximation of low temperature limit. Wear and extreme pressure (EP) properties were determined on the Shell 4-Ball Wear and EP testers, respectively. Wear scar diameters were measured on the three stationary balls after one hour at 600 rev./ min. at 75 C. with 10 kg. and 40 kg. loads using a traveling microscope at 40X. Data are given in Table IX.

TABLE IX.WEAR AND EXTREME PRESSURE MIL-G-10924. b MIL-G-3278. c MIL-G-7l18.

drical hole /2 in. diam. x /2 in. deep) in a block of the test metal. A dowel of test metal in. diam., fiat end) was rotated into the block at 1760 rev./min. under a load of one hundred pounds. The metal combinations tested are given in Table VII. The only combination which showed explosive reactivity was 52100 steel on magnesium. These results have bearing on the use of The values are the average of the readings taken parallel and normal to the scufi marks. The EP properties were determined by measuring the incipient seizure and weld loads. The former is the load at which a sudden sizeable increase in the scar diameter occurs, while the latter is the load at which rotation of the upper ball in relation to the other three is no longer possible. Scar diameters were measured after one minute at each load which was increased in kg. increments to the weld point. A fresh sample and new steel balls were used with each load. Wear and extreme pressure data were compared with corresponding data on typical conventional petroleum and synthetic greases and it may be concluded that the properties in question are comparable.

I claim:

1. An improved grease-type lubricant comprising a mixture of mixed perfluorotrialkylamines, the alkyl groups thereof containing from 4 to 6 carbon atoms, with a thickener selected from the group consisting of tetrafluoroethylene polymers having a molecular weight in the range of 2,000 to 30,000, graphite, and silica.

2. An improved grease-type lubricant consisting essentially of mixed perfiuorotrialkylamines having 4 to 6 carbon atoms in the contained alkyl groups with a thickening amount of tetrafiuoroethylene polymers having a molecular weight in the range of 2,000 to 30,000, said lubricant characterized by excellent physical stability and compatibility with contemporary missile fuels and oxidizers.

3. An improved grease-type lubricant consisting essentially of mixed perfluorotrialkylamines with a thickening amount of tetrafluoroethylene polymers, said perfluorotrialkylamines having 4 to 6 carbon atoms in the contained alkyl groups and said tetrafiuoroethylene polymers having a molecular weight in the range of 2,000 to 30,000, said lubricant characterized by no visible fluid separation on standing for periods up to one year and little separation in cone tests at 100 C. for a period of 30 hours.

4. An improved grease-type lubricant according to claim 3, said lubricant being further characterized by non-reactivity with and insolubility in ethyl alcohol, hydrocarbon fuel, unsymmetrical dimethylhydrazine, diethylenetriamine, a 60:40 mixture of unsymmetrical dimethylhydrazine and diethylenetriamine, aniline, a 50:50 mixture of unsymmetrical dimethy-lhydrazine and hydrazine, hydrazine, 90% hydrogen peroxide, inhibited red fuming nitric acid, and nitrogen tetroxide.

5. An improved grease-type lubricant according to claim 4, said lubricant being further characterized by high impact compatibility with liquid oxygen and nitrogen tetroxide.

6. An improved grease-type lubricant according to .claim 3 wherein said mixed perfluorotrialkylamines are present in an amount ranging from about 71.8 to 82.0% and said tetrafluoroethylene polymers are present in an amount ranging from about 28.2 to 18.0%

7. An improved grease-type lubricant according to claim 3 wherein said perfluorotrialkylamines consist essentially of perfiuorotributylamines.

8. An improved grease-type lubricant according to claim 3 wherein said tetrafluoroethylene polymers have a molecular weight of about 5,000.

9. An improved grease-type lubricant according to claim 3 wherein said tetrafluoroethylene polymers have a molecular weight of about 10,000.

10. An improved grease-type lubricant according to claim 3 wherein said tetrafluoroethylene polymers have a molecular weight of about 30,000.

11. An improved grease-type lubricant comprising a mixture of mixed perfluorotrialkylamines, the alkyl groups thereof containing from 4 to 6 carbon atoms, with graphite.

12. An improved grease-type lubricant according to claim 11 wherein said graphite constitutes about 15% by weight of said mixture.

13. An improved grease-type lubricant comprising a mixture of mixed perfluorotrialkylamines, the alkyl group thereof containing from 4 to 6 carbon atoms, with silica. 14. An improved grease-type lubricant according to claim 13 wherein said silica constitutes about 10% by weight of said mixture.

15. A method of preparing an improved grease-type lubricant consisting essentially of a base fluid and a thickener, said base fluid consisting essentially of mixed perfluorotrialkylamines having 4 to 6 carbon atoms in the contained alkyl groups and said thickener consisting essentially of tetrafluoroethylene polymers having a molecular weight in the range of 2,000 to 30,000, said method comprising the steps of dispersing particles of said thickener in a solvent, evaporating 50 to of said solvent until a viscous dispersion of the consistency of glycerol is obtained,

admixing about 75% of the total quantity of base fiuid with stirring and heating until complete evaporation of said solvent, and

admixing the remainder of the base fluid with stirring until a homogeneous product is obtained.

16. A method according to claim 15 wherein said solvent comprises trichlorotrifluoroethane.

17. A method according to claim 15 wherein said perfluorotrialkylamines comprise perfiuorotributylarnines.

18. A method according to claim 15 wherein said tetrafiuoroethylene polymers have a molecular weight of about 2,000.

19. A method according to claim 15 wherein said tetrafluoroethylene polymers have a molecular weight of about 5,000.

20. A method according to claim 15 wherein said tetrafluoroethylene polymers have a molecular weight of about 10,000.

21. A method according to claim 15 wherein said tetrafluoroethylene polymers have a molecular weight of about 30,000.

References Cited by the Examiner Grease-Type Lubricants Compatible With Missile Fuels and Oxidizers, by Messina, in Industrial and Engineering Chemistry Product Research and Development, vol. 2, No. 3, September 1963, pages 209-212.

DANIEL E. WYMAN, Primary Examiner.

I. VAUGHN, Assistant Examiner. 

1. AN IMPROVED GREASE-TYPE LUBRICANT COMPRISING A MIXTURE OF MIXED PERFLUOROTRIALKYLAMINES, THE ALKYL GROUPS THEREOF CONTAINING FROM 4 TO 6 CARBON ATOMS, WITH A THICKNER SELECTED FROM THE GROUP CONSISTING OF TETRAFLUOROETHYLENE POLMERS HAVING A MOLECULAR WEIGHT IN THE RANGE OF 2,000 TO 30,000, GRAPHITE, AND SILCIA. 